When transmitting information such as documents, drawings, images, or data bases, the data must be transmitted without error and without being wire-tapped by a third party. To accomplish the former objective, error-correcting code technology is used; for the latter, cryptographic technology.
One type of error-correcting code is the block code. Block codes correct errors in transmitted codes by adding redundancy check bits to a given length of information bits. High-correction-capacity error-correcting codes are supplemented by adding even longer check bits. Consequently, data requiring high reliability use high-correction-capacity error-correcting codes, which in turn require longer check bits. Error-correcting capacity involves both correction and detection. The Reed-Solomon code is one such code. The principle of these techniques can be found in "Error-Correcting Codes"by W. W. Peterson and E. J. Weldon, Jr., 2nd ed.,pp. 269-309, MIT press, Cambridge, Massachusetts, 1972.
With tile increasing number of computer end users, sharing of common system resources such as files, programs, and hardware and the increasing use of distribution systems or networks, larger and more complex computer base information systems are being created. Therefore, wiretapping has become simpler, making tile use of encryption devices necessary to prevent it.
Cryptography deals with methods by which message data called plain text is enciphered into unintelligible data called cipher text and by which the cipher text is deciphered back into plain text. The encipherment/decipherment transformations are carried out by a cipher algorithm controlled in accordance with a cipher key. The publication "Block Cipher System for Data Security" is described in U.S. Pat. No. 3,958,081 issued May 18, 1976. The algorithm described therein was adopted by the National Bureau of Standards as a data encryption standard (DES) algorithm and is described in detail in the Federal Information Processing Standards publication, Jan. 15, 1977, FIPS PUB 46. The DES is a 64-bit block encipherment algorithm. A similar code is the FEAL-8 . This algorithm is described in "Fast Data Encipherment Algorithm FEAL-8 by S.Miyaguchi, A. Shiraishi, and A. Shimizu, REVIEW of the Electrical Communication Laboratories, Vol. 36, No.4, pp. 433-437, 1988.
In addition to the above symmetrical encipherments (in which both enciphering and deciphering keys are equal), asymmetrical public-key encipherments (for example, RSA) also are in use. The latter encipherments are for message authentification, in other words, they are used to acknowledge the sender of a message. They can also be used in digital signature algorithms. For example, a digital signature method that utilizes the RSA encipherment works as follows. First, signatory A uses one-way function H to generate H(M) from message M. Then signatory A, using a secret encipher key, enciphers H(M) to create a digital signature, and then sends that signature along with message M to addressees B, C, etc. Addressees B, C, etc. utilize public deciphering keys to change the digital signature into plain text. If the plain text is produced correctly, the message sender, A, can be accurately identified. Furthermore, with a one-way function, H(M) can be easily calculated; however, the computation of M from H(M) is difficult. This function is used to detect unauthorized changes in message M. RSA encipherment is described in "A Method for Obtaining Digital Signatures and Public-key Cryptosystems," Communications of the ACM, Vol. 21, No. 2 , pp. 120-126 (1978).
These techniques are superior and are applied in such areas as electronic documents, data bases, and IC cards. This invention uses these techniques as its foundation. Adoption of these techniques does not, however, limit the invention; the invention can apply various types of error-correcting codes and encrypting techniques.
Information security measures are indispensable. The transmission and processing of information such as secret documents, drawings, images, and data bases is mainly accomplished after line level encipherment or full text file encipherment.
Next, the detection and correction of errors produced during actual data transmission is accomplished with error-correcting codes. Normally, a record utilizes a type of error-correcting codes. Methods of using error-correcting codes with relation to the importance of words has been proposed in "A Mapping Scheme of Error-Correcting Codes According to Importance of Natural language Words," written by T. Sasaki, R. Kohno, and H. Imai in the 1990 Autumn National Convention Record, The Institute of Electronics, Information and Communication Engineers, part 1, p.162, Oct. 15, 1990 (in Japanese).
Also, computer management of filing and data bases is accomplished with access control through passwords, with access authority being given for each file, record, and field. That is, to perform an operation such as read/write of a file, the user must first input the password. After that is registered, the right to utilize the desired information is checked; only upon passing this check is operation approval given to the user.
The publication "Method for Providing Information Security Protocols to an Electronic Calendar" is described in U.S. Pat. No. 4,881,179 issued Nov. 14, 1989. In the method described therein, security classifications are assigned to calendar entries. A calendar owner can then selectively display or print calendar event descriptions having assigned security classifications below a given access level. This method, however, does not use encipherment.
In general, information such as documents, drawings, images, and data bases can be thought of as containing the attributes reliability and confidentiality. For example, money requires a high degree of reliability, whereas a simple greeting requires only minimal reliability; in other words, an amount of error is permitted. Furthermore, security protection may be required for a certain time period, such as when protecting the sales price and period of new product. In a case such as this, a high degree of security would probably be demanded. Conventional data transmission and processing have ignored reliability and confidentiality attributes possessed by each portion of data and encoded or enciphered the data in a lump. As a consequense, intellectually efficient data transmission and processing, which utilizes the informational attributes of data, cannot be realized and processing speed decreases.
Also, data records are enciphered in each field. Users cannot, however, freely change those enciphered fields nor can they select and encipher a certain portion of given field's data on the screen, for example. Further, when a document is to be enciphered and transmitted, it is normally enciphered after a secretary has completed the document. Similarly, when it is to be line-level enciphered and transmitted, the operator may be able to view the plain text.
Additionally, security managers control these encipherment processes and have access to all encrypted messages. However, it is not desirable for information managers or operators to have access to confidential information such as personnel data bases.
Conventional technology in particular does not process information in accordance with the information'attributes of reliability and/or confidentiality. Another serious problem is the difficulty for the user of getting used to and using the error-correcting codes and/or cryptography. Consequently, a flexible system that uses error-correcting codes and/or cryptography and is superior to man-machine interface cannot be developed.
The present invention implements some methods to overcome the above described problems.